Calcium independent cytosolic phospholipase A2/B enzymes

ABSTRACT

The invention provides a novel calcium-independent cytosolic phospholipase A 2 /B enzyme, polynucleotides encoding such enzyme and methods for screening unknown compounds for anti-inflammatory activity mediated by the arachidonic acid cascade.

This application is a continuation-in-part of application Ser. No. 08/281,193, filed Jul. 27, 1994.

The present invention relates to a purified calcium independent cytosolic phospholipase A₂/B enzymes which are useful for assaying chemical agents for anti-inflammatory activity.

BACKGROUND OF THE INVENTION

The phospholipase A, enzymes comprise a widely distributed family of enzymes which catalyze the hydrolysis of the acyl ester bond of glycerophospholipids at the sn-2 position. One kind of phospholipase A₂ enzymes, secreted phospholipase A₂ or sPLA₂, are involved in a number of biological functions, including phospholipid digestion, the toxic activities of numerous venoms, and potential antibacterial activities. A second kind of phospholipase A, enzymes, the intracellular phospholipase A₂ enzymes, also known as cytosolic phospholipase A₂ or cPLA₂, are active in membrane phospholipid turnover and in regulation of intracellular signalling mediated by the multiple components of the well-known arachidonic acid cascade. One or more cPLA₂ enzymes are believed to be responsible for the rate limiting step in the arachidonic acid cascade, namely, release of arachidonic acid from membrane glycerophospholipids. The action of cPLA₂ also results in biosynthesis of platelet activating factor (PAF).

The phospholipase B enzymes are a family of enzymes which catalyze the hydrolysis of the acyl ester bond of glycerophospholipids at the sn-1 and sn-2 positions. The mechanism of hydrolysis is unclear but may consist of initial hydrolysis of the sn-2 fatty acid followed by rapid cleavage of the sn-1 substituent, i.e. functionally equivalent to the combination of phospholipase A₂ and lysophospholipase (Saito et al., Methods of Enzymol., 1991, 197, 446; Gassama-Diagne et al., J. Biol. Chem., 1989, 264, 9470). Whether these two events occur at the same or two distinct active sites has not been resolved. It is also unknown if these enzymes have a preference for the removal of unsaturated fatty acids, in particular arachidonic acid, at the sn-2 position and accordingly contribute to the arachidonic acid cascade.

Upon release from the membrane, arachidonic acid may be metabolized via the cyclooxygenase pathway to produce the various prostaglandins and thromboxanes, or via the lipoxygenase pathway to produce the various leukotrienes and related compounds. The prostaglandins, leukotrienes and platelet activating factor are well known mediators of various inflammatory states, and numerous anti-inflammatory drugs have been developed which function by inhibiting one or more steps in the arachidonic acid cascade. Use of the present anti-inflammatory drugs which act through inhibition of arachidonic acid cascade steps has been limited by the existence of side effects which may be harmful to various individuals.

A very large industrial effort has been made to identify additional anti-inflammatory drugs which inhibit the arachidonic-acid cascade. In general, this industrial effort has employed the secreted phospholipase A₂ enzymes in inhibitor screening assays, for example, as disclosed in U.S. Pat. No. 4,917,826. However, because the secreted phospholipase A₂ enzymes are extracellular proteins (i.e., not cytosolic) and are not specific for hydrolysis of arachidonic acid, they are presently not believed to participate directly in the arachidonic acid cascade. While some inhibitors of the small secreted phospholipase A₂ enzymes have anti-inflammatory action, such as indomethacin, bromphenacyl bromide, mepacrine, and certain butyrophenones as disclosed in U.S. Pat. No. 4,239,780, it is presently believed that inhibitor screening assays should employ cytosolic phospholipase A₂ enzymes which directly participate in the arachidonic acid cascade.

An improvement in the search for anti-inflammatory drugs which inhibit the arachidonic acid cascade was developed in commonly assigned U.S. Pat. No. 5,322,776, incorporated herein by reference. In that application, a cytosolic form of phospholipase A₂ was identified, isolated, and cloned. Use of the cytosolic form of phospholipase A₂ to screen for anti-inflammatory drugs provides a significant improvement in identifying inhibitors of the arachidonic acid cascade. The cytosolic phospholipase A₂ disclosed in U.S. Pat. No. 5,322,776 is a 110 kD protein which depends on the presence of elevated levels of calcium inside the cell for its activity. The cPLA₂ of U.S. Pat. No. 5,322,776 plays a pivotal role in the production of leukotrienes and prostaglandins initiated by the action of pro-inflammatory cytokines and calcium mobilizing agents. The cPLA₂ of U.S. Pat. No. 5,322,776 is activated by phosphorylation on serine residues and increasing levels of intracellular calcium, resulting in translocation of the enzyme from the cytosol to the membrane where arachidonic acid is selectively hydrolyzed from membrane phospholipids.

In addition to the cPLA₂ of U.S. Pat. No. 5,322,776, some cells contain calcium independent phospholipase A₂/B enzymes. For example, such enzymes have been identified in rat, rabbit, canine and human-heart tissue (Gross, T C M, 1991, 2, 115; Zupan et al., J. Med. Chem., 1993, 36, 95; Hazen et al., J. Clin. Invest., 1993, 91, 2513; Lehman et al., J. Biol. Chem., 1993, 268, 20713; Zupan et al., J. Biol. Chem., 1992, 267, 8707; Hazen et al., J. Biol. Chem., 1991, 266, 14526; Loeb et al., J. Biol. Chem., 1986, 261, 10467; Wolf et al., J. Biol. Chem., 1985, 260, 7295; Hazen et al., Meth. Enzymol., 1991, 197, 400; Hazen et al., J. Biol. Chem., 1990, 265, 10622; Hazen et al., J. Biol. Chem., 1993, 268, 9892; Ford et al., J. Clin. Invest., 1991, 88, 331; Hazen et al., J. Biol. Chem., 1991, 266, 5629; Hazen et al., Circulation Res., 1992, 70, 486; Hazen et al., J. Biol. Chem., 1991, 266, 7227; Zupan et al., FEBS, 1991, 284, 27), as well as rat and human pancreatic islet cells (Ramanadham et al., Biochemistry, 1993, 32, 337; Gross et al., Biochemistry, 1993, 32, 327), in the macrophage-like cell line, P388D₁ (Ulevitch et al., J. Biol. Chem., 1988, 263, 3079; Ackermann et al., J. Biol. Chem., 1994, 269, 9227; Ross et al., Arch. Biochem. Biophys., 1985, 238, 247; Ackermann et al., FASEB Journal, 1993, 7(7), 1237), in various rat tissue cytosols (Nijssen et al., Biochim. Biophys. Acta, 1986, 876, 611; Pierik et al., Biochim. Biophys. Acta, 1988, 962, 345; Aarsman et al., J. Biol. Chem., 1989, 264, 10008), bovine brain (Ueda et al., Biochem. Biophys, Res. Comm., 1993, 195, 1272; Hirashima et al., J. Neurochem., 1992, 59, 708), in yeast (Saccharomyces cerevisiae) mitochondria (Yost et al., Biochem. International, 1991, 24, 199), hamster heart cytosol (Cao et al., J. Biol. Chem., 1987, 262, 16027), rabbit lung microsomes (Angle et al., Biochim. Biophys. Acta, 1988, 962, 234) and guinea pig intestinal brush-border membrane (Gassama-Diagne et al., J. Biol. Chem., 1989, 264, 9470).

It is believed that the calcium independent phospholipase A₂/B enzymes may perform important functions in release of arachidonic acid in specific tissues which are characterized by unique membrane phospholipids, by generating lysophospholipid species which are deleterious to membrane integrity or by remodeling of unsaturated species of membrane phospholipids through deacylation/reacylation mechanisms. The activity of such a phospholipase may well be regulated by mechanisms that are different from that of the cPLA₂ of U.S. Pat. No. 5,322,776. In addition the activity may be more predominant in certain inflamed tissues over others. Although the enzymatic activity is not dependent on calcium this does not preclude a requirement for calcium in vivo, where the activity may be regulated by the interaction of other protein(s) whose function is dependent upon a calcium flux.

SUMMARY OF THE INVENTION

In certain embodiments, the present invention provides compositions comprising a purified phospholipase enzyme characterized by (a) activity in the absence of calcium; (b) a molecular weight of 86 kD on SDS-PAGE; and (c) the presence of one or more amino acid sequences selected from the group consisting of NPHSGFR (SEQ ID NO:3), XASXGLNQVNK (SEQ ID NO:4) (X is preferably N or A), YGASPLHXAK (SEQ ID NO:5) (X is preferably W), DNMEMIK (SEQ ID NO:6), GVYFR (SEQ ID NO:7), MKDEVFR (SEQ ID NO:8), EFGEHTK (SEQ ID NO:9), VMLTGTLSDR (SEQ ID NO:10), XYDAPEVIR (SEQ ID NO: 11) (X is preferably N), FNQNINLKPPTQPA (SEQ ID NO:12), XXGAAPTYFRP (SEQ ID NO:13) (X is preferably S), TVFGAK (SEQ ID NO: 14), and XWSEMVGIQYFR (SEQ ID NO: 15) (X is preferably A), wherein X represents any amino acid residue.

In other embodiments, the invention provides compositions comprising a purified phospholipase enzyme characterized by (a) activity in the absence of calcium; (b) a molecular weight of 86 kD on SDS-PAGE; and (c) the presence of one or more amino acid sequences selected from the group consisting of YGASPLHXAK, MKDEVFR, EFGEHIK, VMLTGTLSDR, XXGAAPTYFRP and TVFGAK, wherein X represents any amino acid residue.

Certain embodiments provide compositions comprising a purified mammalian calcium independent phospholipase A₂/B enzyme.

In other embodiments, the enzyme is further characterized by activity in a mixed micelle assay with 1-palmitoyl-2-[¹⁴C]-arachidonyl-phosphatidylcholine (preferably a specific activity of about 1 μmol to about 20 μmol per minute per milligram, more preferably a specific activity of about 1 μmol to about 5 μmol per minute per milligram); by a pH optimum of 6; and/or by the absence of stimulation by adenosine triphosphate in the liposome assay.

In other embodiments, the invention provides isolated polynucleotides comprising a nucleotide sequence selected from the group consisting of: (a) the nucleotide sequence of SEQ ID NO: 1; (b) a nucleotide sequence encoding the amino acid sequence of SEQ ID NO:2; (c) a nucleotide sequence encoding a fragment of the amino acid sequence of SEQ ID NO:2 having activity in a mixed micelle assay with 1-palmitoyl-2-[¹⁴C]-arachidonyl-phosphatidylcholine; (d) a nucleotide sequence capable of hybridizing with the sequence of (a), (b) or (c) which encodes a peptide having activity in a mixed micelle assay with 1-palmitoyl-2-[¹⁴C]-arachidonyl-phosphatidylcholine; and (e) allelic variants of the sequence of (a). Other embodiments provide an isolated polynucleotide comprising a nucleotide sequence selected from the group consisting of: (a) the nucleotide sequence of SEQ ID NO: 16; (b) a nucleotide sequence encoding the amino acid sequence of SEQ ID NO: 17; (c) a nucleotide sequence encoding a fragment of the amino acid sequence of SEQ. ID NO: 17 having activity in a mixed micelle assay with 1-palmitoyl-2-[¹⁴C]-arachidonyl-phosphatidylcholine; (d) the nucleotide sequence of SEQ ID NO: 18; (e) a nucleotide sequence encoding the amino acid sequence of SEQ ID NO: 19; (f) a nucleotide sequence encoding a fragment of the amino acid sequence of SEQ ID NO: 19 having activity in a mixed micelle assay with 1-palmitoyl-2-[¹⁴C]-arachidonyl-phosphatidylcholine; (g) the nucleotide sequence of SEQ ID NO:20; (h) a nucleotide sequence encoding the amino acid sequence of SEQ ID NO:21; (i) a nucleotide sequence encoding a fragment of the amino acid sequence of SEQ ID NO:21 having activity in a mixed micelle assay with 1-palmitoyl-2-[¹⁴C]-arachidonyl-phosphatidylcholine; (O) the nucleotide sequence of SEQ ID NO:22; (k) a nucleotide sequence encoding the amino acid sequence of SEQ ID NO:23; (l) a nucleotide sequence encoding a fragment of the amino acid sequence of SEQ ID NO:23 having activity in a mixed micelle assay with 1-palmitoyl-2-[¹⁴C]-arachidonyl-phosphatidylcholine; (m) a nucleotide sequence capable of hybridizing with the sequence of any of (a)-(l) which encodes a peptide having activity in a mixed micelle assay with 1-palmitoyl-2-[¹⁴C]-arachidonyl-phosphatidylcholine; and (n) allelic variants of the sequence of (a), (d), (g) or (j). Expression vectors comprising such polynucleotides and host cells f transformed with such vectors are also provided by the present invention. Compositions comprising peptides encoded by such polynucleotides are also provided.

The present invention also provides processes for producing a phospholipase enzyme, said process comprising: (a) establishing a culture of the host cell transformed with a cPLA₂/B encoding polynucleotide in a suitable culture medium; and (b) isolating said enzyme from said culture. Compositions comprising a peptide made according to such processes are also provided.

Certain embodiments of the present invention provide compositions comprising a peptide comprising an amino acid sequence selected from the group consisting of: (a) the amino acid sequence of SEQ ID NO:2; and (b) a fragment of the amino acid sequence of SEQ ID NO:2 having activity in a mixed micelle assay with 1-palmitoyl-2-[¹⁴C]-arachidonyl-phosphatidylcholine.

Other embodiments provide compositions comprising a peptide comprising an amino acid sequence selected from the group consisting of: (a) the amino acid sequence of SEQ ID NO: 17; (b) a fragment of the amino acid sequence of SEQ ID NO:17 having activity in a mixed micelle assay with 1-palmitoyl-2-[¹⁴C]-arachidonyl-phosphatidylcholine; (c) the amino acid sequence of SEQ ID NO: 19; (d) a fragment of the amino acid sequence of SEQ ID NO: 19 having activity in a mixed micelle assay with 1-palmitoyl-2-[¹⁴C]-arachidonyl-phosphatidylcholine; (e) the amino acid sequence of SEQ ID NO:21; (f) a fragment of the amino acid sequence of SEQ ID NO:21 having activity in a mixed micelle assay with 1-palmitoyl-2-[¹⁴C]-arachidonyl-phosphatidylcholine; (g) the amino acid sequence of SEQ ID NO:23; and (h) a fragment of the amino acid sequence of SEQ ID NO:23 having activity in a mixed micelle assay with 1-palmitoyl-2-[¹⁴C]-arachidonyl-phosphatidylcholine.

The present invention also provides methods for identifying an inhibitor of phospholipase activity, said method comprising: (a) combining a phospholipid, a candidate inhibitor compound, and a composition comprising a phospholipase enzyme peptide; and (b) observing whether said phospholipase enzyme peptide cleaves said phospholipid and releases fatty acid thereby, wherein the peptide composition is one of those described above. Inhibitor of phospholipase activity identified by such methods, pharmaceutical compositions comprising a therapeutically effective amount of such inhibitors and a pharmaceutically acceptable carrier, and methods of reducing inflammation by administering such pharmaceutical compositions to a mammalian subject are also provided.

Polyclonal and monoclonal antibodies to the peptides of the invention are also provided.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1: Fractions containing activity eluted from a Mono P column were examined by reducing SDS-PAGE on a 420% gradient gel. Activity of each fraction is show above the gel and the 86 kD band is indicated on the silver stained gel. Molecular weight markers are indicated.

FIG. 2: Active fractions from a Mono p/Heparin column were combined and further purified on a size exclusion column. Activity eluted in the 250-350 kD size range. Examination of the fractions by SDS-PAGE under reducing conditions on 420% gel indicated only one protein band correlated with activity at 86 kD. Molecular weight markers are indicated.

FIG. 3: Active fractions from Mono P eluate and cPLA₂ (0.1-1.0 μg) were analyzed on two 420% SDS gels under reducing conditions run in parallel. One gel was silver stained (A) and in the other gel the proteins were transferred to nitrocellulose. the blot was than probed with an anti-cPLA, polyclonal antibody and reactive proteins were visual with the ECL system (Amersham) (B). Molecular weight markers are indicated.

FIG. 4: The activity of the calcium-independent phospholipase eluted from a Mono P/Heparin column and cPLA₂ were compared under conditions which favor each enzyme; pH 7, 10% glycerol in the absence of calcium and pH 9, 70% glycerol in the presence of calcium, respectively.

FIG. 5: Activity in the cytosolic extracts of COS cells transfected with: no DNA; plasmid (pED) containing no inserted gene; clone 9 in the antisense orientation; and clones 49, 31 and 9 expressed in pED. The extracts were analyzed under two different assay conditions described for the data presented in FIG. 4.

FIG. 6: A comparison of sn-2 fatty acid hydrolysis by activity eluted from a Mono P/Heparin column as a function of the fatty acid substituent at either the sn-1 or sn-2 position and the head group. HAPC, SAPC, PLPC, POPC, PPPC, LYSO and PAPC indicate 1-hexadecyl-2-arachidonyl-, 1-stearoyl-2-arachidonyl-, 1-palmitoyl-2-linoleyl-, 1-palmitoyl-2-oleyl-, 1-palmitoyl-2-palmitoyl-, 1-palmitoyl-, 1-palmitoyl-2-arachidonyl-phosphatidylcholine, respectively. PAPE and SAPI indicate 1-palmitoyl-2-arachidonyl-phosphotidylethanolamine and 1-stearoyl-2-arachidonyl-phosphoinositol, respectively. In all cases the ¹⁴C-labelled fatty acid is in the sn-2 position.

FIG. 7: A 4-20% SDS-PAGE of lysates (5×10¹⁰ cpm/lane) of ³⁵S-methionine labelled COS cells transfected with, no DNA, pED (no insert), clone 9 reverse orientation, clones 9, 31 and 49; lanes 1-6, respectively. Molecular weight markers are indicated.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have found surprisingly a calcium independent cytosolic phospholipase enzyme, designated calcium independent cytosolic phospholipase A₂/B or calcium independent cPLA₂/B, purified from the cytosol of Chinese hamster ovary (CHO) cells. The activity was also present in the cytosol of tissues and cell extracts listed in Table I. TABLE I mixed micelle pH 7 liposome pH 7 tissue/cell (pmol/min/mg) (pmol/min/mg) rat brain 1-2 rat heart 0.3-0.5 bovine brain 0.4 pig heart 0.8 CHO-Dukx 10-20 2-5 U937 (ATCC CRL1593) 2 FBHE (ATCC CRL1395) 2 H9c2 (ATCC Ccl 108) 15

The enzyme was originally purified by more than 8,000-fold from CHO cells by sequential chromatography on diethylaminoethane (DEAE), phenyl and heparin-toyopearl, followed by chromatofocussing on Mono P (as described further in Example 1). In addition the activity could be further purified by size exclusion chromatography after the Mono P column. The enzyme eluted from the size exclusion chromatography column in the 250-350 kD range, indicating the active enzyme may consist of a multimeric complex, or may possibly be associated with phospholipids.

The calcium independent phospholipase activity correlated with a single major protein band of 86 kD on denaturing sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of active fractions from the Mono P and size exclusion chromatographic steps; in the latter no protein bands were observed in the 250-350 kD range. The specific activity of the enzyme is about 1 μmol to about 20 μmol per minute per milligram based on the abundance of the 86 kD band in the most active fractions eluted from the Mono P and size exclusion columns in the mixed micelle assay (Example 3B). The protein band was not recognized by a polyclonal antibody directed against the calcium dependent cPLA₂ of U.S. Pat. No. 5,322,776.

The calcium independent phospholipase of the present invention has a pH optimum of 6; its activity is suppressed by calcium (in all assays) and by triton X-100 (in the assay of Example 3A); and is not stimulated by adenosine triphosphate (ATP) (in the assay of Example 3A). The enzyme is inactivated by high concentration denaturants, e.g. urea above 3M, and by detergents, e.g. CHAPS and octyl glucoside. The calcium-independent phospholipase favors hydrolysis by several fold of unsaturated fatty acids, e.g. linoleyl, oleyl and arachidonyl, at the sn-2 position of a phospholipid compared with palmitoyl. In addition there is a preference for palmitoyl at the sn-1-position over hexadecyl or stearoyl for arachidonyl hydrolysis at the sn-2 position in terms of head group substituents there is a clear preference for inositol over choline or ethanolamine when arachidonyl is being hydrolyzed at the sn-2 position. Further, as with cPLA₂ of U.S. Pat. No. 5,322,776, there is a significant lysophospholipase activity, i.e. hydrolysis of palmitoyl at the sn-1 position when there is no fatty acid substituent at the sn-2 position. Finally, hydrolysis of fatty acid substituents in the sn-1 or sn-2 in PAPC were compared where either palmitoyl or arachidonyl were labelled with ¹⁴C. Fatty acids were removed at both positions with the sn-2 position having a higher initial rate of hydrolysis by 2-3 fold. This result may indicate sequential hydrolysis of the arachidonyl substituent followed by rapid cleavage of palmitoyl in the lysophospholipid species, which is suggested by the hydrolysis of the individual lipid species. The similar rates of hydrolysis of fatty acid substituents at the sn-1 (palmitoyl) or sn-2 (arachidonyl) positions, where the radioactive label is in either position, is indicative of a phospholipase B activity. However, the fatty acid substituent at the sn-2 position clearly influences the PLB activity, not the sn-1 fatty acid, since hydrolysis of 1,2-dipalmitoyl substituted phospholipids is substantially less than for the 1-palmitoyl-2-arachidonyl species. These results can be clarified by studying the hydrolysis rates at each position of isotopically dual labelled phospholipids, e.g. ³H and ¹⁴C containing fatty acids at the sn-1 and sn-2 positions, respectively. Therefore, it is prudent to designate the enzyme as a phospholipase A₂/B.

A cDNA encoding the calcium independent cPLA₂/B of the present invention was isolated as described in Example 4. The sequence of the cDNA is reported as SEQ ID NO: 1. The amino acid sequence encoded by such cDNA is SEQ ID NO:2. The invention also encompasses allelic variations of the cDNA sequence as set forth in SEQ ID NO:1, that is, naturally-occurring alternative forms of the cDNA of SEQ ID NO: 1 which also encode phospholipase enzymes of the present invention.

Other cDNAs encoding a calcium independent cPLA₂/B of the present invention were isolated from human cDNA sources. Two clones identified as “19a” and “19b” were isolated from a Raij cell DNA library derived from Burkitt's lymphoma (ATCC CCL86, commercially available from Clonetech) using a probe derived from the CHO sequence (a 2.1 kb SalI-SmaI fragment). Clones 19a and 19b were deposited with the American Type Culture Collection on Nov. 7, 1995 as accession numbers ATCC and ATCC M The nucleotide sequences of clones 19a and 19b are reported in SEQ ID NO: 16 and SEQ ID NO:18, respectively. SEQ ID NO:17 and SEQ ID NO:18 port the corresponding amino acid sequences encoded by the coding regions of clones 19a and 19b, respectively. Clones 19a and 19b are both partial clones of the full-length human enzyme.

SEQ ID NO:20 and SEQ ID NO:22 report the nucleotide sequences of alternative ways in which clones 19a and 19b can be spliced to encode a longer partial clone for the full-length human enzyme. The splice occurs after nucleotide 1225 in SEQ ID NO:20 and after nucleotide 1228 in SEQ ID NO:22. The corresponding spliced amino acid sequences are reported in SEQ ID NO:21 and SEQ ID NO:23. Spliced cDNA clones can be made from clones 19a and 19b in accordance with methods known to those skilled in the art.

Full-length clones encoding the human enzyme can be isolated by probing human cDNA libraries containing full-length clones using probes derived from SEQ ID NO: 16, SEQ ID NO:18, SEQ ID NO:20 or SEQ ID NO:22.

Also included in the invention are isolated DNAs which hybridize to the DNA sequence set forth in SEQ ID NO: 1, SEQ ID NO: 16, SEQ ID NO: 18, SEQ ID: NO:20 or SEQ ID NO:22 under stringent (e.g. 4×SSC at 65° C. or 50% formamide and 4×SSC at 42° C.), or relaxed (4×SSC at 50° C. or 30-40% form amide at 42° C.) conditions.

The isolated polynucleotides of the invention may be operably linked to an expression control sequence such as the pMT2 or pED expression vectors disclosed in Kaufman et al., Nucleic Acids Res. 19, 44854490 (1991), in order to produce the phospholipase enzyme peptides recombinantly. Many suitable expression control sequences are known in the art. General methods of expressing recombinant proteins are also known and are exemplified in R. Kaufman, Methods in Enzymology 185, 537-566 (1990). As defined herein “operably linked” means enzymatically or chemically ligated to form a covalent bond between the isolated polynucleotide of the invention and the expression control sequence, in such a way that the phospholipase enzyme peptide is expressed by a host cell which has been transformed (transfected) with the ligated polynucleotide/expression control sequence.

A number of types of cells may act as suitable host cells for expression of the phospholipase enzyme peptide. Suitable host cells are capable of attaching carbohydrate side chains characteristic of functional phospholipase enzyme peptide. Such capability may arise by virtue of the presence of a suitable glycosylating enzyme within the host cell, whether naturally occurring, induced by chemical mutagenesis, or through transfection of the host cell with a suitable expression plasmid containing a polynucleotide encoding the glycosylating enzyme. Host cells include, for example, monkey COS cells, Chinese Hamster Ovary (CHO) cells, human kidney 293 cells, human epidermal A431 cells, human Colo205 cells, 3T3 cells, CV-1 cells, other transformed primate cell lines, normal diploid cells, cell strains derived from in vitro culture of primary tissue, primary explants, HeLa cells, mouse L cells, BHK, HL-60, U937, or HaK cells.

The phospholipase enzyme peptide may also be produced by operably linking the isolated polynucleotide of the invention to suitable control sequences in one or more insect expression vectors, and employing an insect expression system. Materials and methods for baculovirus/insect cell expression systems are commercially available in kit form from, e.g., Invitrogen, San Diego, Calif., U.S.A. (the MaxBac® kit), and such methods are well known in the art, as described in Summers and Smith, Texas Agricultural Experiment Station Bulletin No. 1555 (1987), incorporated herein by reference.

Alternatively, it may be possible to produce the phospholipase enzyme peptide in lower eukaryotes such as yeast or in prokaryotes such as bacteria. Potentially suitable yeast strains include Saccharomyces cerevisiae. Schizosaccharomyces pombe, Kluyveromyces strains. Candida, or any yeast strain capable of expressing heterologous proteins. Potentially suitable bacterial strains include Escherichia coli, Bacillus subtilis, Salmonella typhimurium, or any bacterial strain capable of expressing heterologous proteins. If the phospholipase enzyme peptide is made in yeast or bacteria, it is necessary to attach the appropriate carbohydrates to the appropriate sites on the protein moiety covalently, in order to obtain the glycosylated phospholipase enzyme peptide. Such covalent attachments may be accomplished using known chemical or enzymatic methods.

The phospholipase enzyme peptide of the invention may also be expressed as a product of transgenic animals, e.g., as a component of the milk of transgenic cows, goats, pigs, or sheep which are characterized by somatic or germ cells containing a polynucleotide encoding the phospholipase enzyme peptide.

The phospholipase enzyme peptide of the invention may be prepared by culturing transformed host cells under culture conditions necessary to express a phospholipase enzyme peptide of the present invention. The resulting expressed protein may then be purified from culture medium or cell extracts as described in the examples below.

Alternatively, the phospholipase enzyme peptide of the invention is concentrated using a commercially available protein concentration filter, for example, an Amicon or Millipore Pellicon ultrafiltration unit. Following the concentration step, the concentrate can be applied to a purification matrix such as a gel filtration medium. Alternatively, an anion exchange resin can be employed, for example, a matrix or substrate having pendant diethylaminoethyl (DEAE) groups. The matrices can be acrylamide, agarose, dextran, cellulose or other types commonly employed in protein purification. Alternatively, a cation exchange step can be employed. Suitable cation exchangers include various insoluble matrices comprising sulfopropyl or carboxymethyl groups. Sulfopropyl groups are preferred (e.g., S-Sepharose® columns). The purification of the phospholipase enzyme peptide from culture supernatant may also include one or more column steps over such affinity resins as concanavalin A-agarose, heparin-toyopearl® or Cibacrom blue 3GA Sepharose®; or by hydrophobic interaction chromatography using such resins as phenyl ether, butyl ether, or propyl ether; or by immunoaffinity chromatography.

Finally, one or more reverse-phase high performance liquid chromatography (RP-HPLC) steps employing hydrophobic RP-HPLC media, e.g., silica gel having pendant methyl or other aliphatic groups, can be employed to further purify the phospholipase enzyme peptide. Some or all of the foregoing purification steps, in various combinations, can also be employed to provide a substantially homogeneous isolated recombinant protein. The phospholipase enzyme peptide thus purified is substantially free of other mammalian proteins and is defined in accordance with the present invention as “isolated phospholipase enzyme peptide”.

The calcium independent cPLA₂/B of the present invention is distinct from the cPLA₂ of U.S. Pat. No. 5,322,776 and from previously-described calcium independent phospholipase A₂ enzymes (such as those described by Gross et al., supra; and Ackermann et al., supra). The enzyme of the present invention differs from the cPLA₂ of the '776 patent in the following ways:

-   -   (1) its activity is not calcium dependent;     -   (2) it is more active in 10% glycerol than in 70% glycerol;     -   (3) it has a molecular weight of 86 kD, not 110 kD as for cPLA₂;     -   (4) it has a pH optimum of 6, not greater than 8 as for cPLA₂;     -   (5) it hydrolyzes fatty acids at sn-1 as well as sn-2;     -   (6) it binds to heparin, while cPLA₂ does not;     -   (7) it elutes from an anion exchange column at 0.1-0.2 M NaCl,         while cPLA₂ elutes at 0.3-0.4 M NaCl; and     -   (8) it does not bind to anti-cPLA₂ polyclonal antibody.         The enzyme of the present invention differs from the calcium         independent enzyme of Gross et al. in the following         characteristics:     -   (1) it has a molecular weight of 86 kD, not 40 kD as for the         Gross enzyme;     -   (2) it is not homologous at the protein level to rabbit skeletal         muscle phosphofructokinase in contrast to the 85 kD putative         regulatory protein associated with the 40 kD Gross enzyme;     -   (3) hydrolysis at the sn-2 position is favored by an acyl-linked         fatty acid at the sn-1 position in contrast to ether-linked         fatty acids with the Gross enzyme;     -   (4) its does not bind to an ATP column and was not activated by         ATP in a liposome assay compared to the Gross enzyme; and     -   (5) it was active in a mixed micelle assay containing Triton         X-100.         The enzyme of the present invention differs from the calcium         independent enzyme of Ackermann et al. (the “Dennis enzyme”) in         the following characteristics:     -   (1) it does not bind to an ATP column;     -   (2) it binds to an anion exchange column (mono Q), while the         Dennis enzyme remains in the unbound fraction;     -   (3) it has a molecular weight of 86 kD, not 74 kD as for the         Dennis enzyme;     -   (4) it has substantial lysophospholipase activity and is         relatively inactive on phospholipids containing ether-linked         fatty acids at the sn-1 position in a liposome assay; and     -   (5) it appears to hydrolyze fatty acid substituents at the sn-1         and sn-2 positions of a phospholipid, whereas the Dennis enzyme         favors hydrolysis at the sn-2 position.

The calcium independent cPLA₂/B of the present invention may be used to screen unknown compounds having anti-inflammatory activity mediated by the various components of the arachidonic acid cascade. Many assays for phospholipase activity are known and may be used with the calcium independent phospholipase A₂/B on the present invention to screen unknown compounds. For example, such an assay may be a mixed micelle assay as described in Example 3. Other known phospholipase activity assays include, without limitation, those disclosed in U.S. Pat. No. 5,322,776. These assays may be performed manually or may be automated or robotized for faster screening. Methods of automation and robotization are known to those skilled in the art.

In one possible screening assay, a first mixture is formed by combining a phospholipase enzyme peptide of the present invention with a phospholipid cleavable by such peptide, and the amount of hydrolysis in the first mixture (B₀) is measured. A second mixture is also formed by combining the peptide, the phospholipid and the compound or agent to be screened, and the amount of hydrolysis in the second mixture (B) is measured. The amounts of hydrolysis in the first and second mixtures are compared, for example, by performing a B/B_(o) calculation. A compound or agent is considered to be capable of inhibiting phospholipase activity (i.e., providing anti-inflammatory activity) if a decrease in hydrolysis in the second mixture as compared to the first mixture is observed. The formulation and optimization of mixtures is within the level of skill in the art, such mixtures may also contain buffers and salts necessary to enhance or to optimize the assay, and additional control assays may be included in the screening assay of the invention.

Other uses for the calcium independent cPLA₂/B of the present invention are in the development of monoclonal and polyclonal antibodies. Such antibodies may be generated by employing purified forms of the calcium independent cPLA₂ or immunogenic fragments thereof as an antigen using standard methods for the development of polyclonal and monoclonal antibodies as are known to those skilled in the art. Such polyclonal or monoclonal antibodies are useful as research or diagnostic tools, and further may be used to study phospholipase A₂ activity and inflammatory conditions.

Pharmaceutical compositions containing anti-inflammatory agents (i.e., inhibitors) identified by the screening method of the present invention may be employed to treat, for example, a number of inflammatory conditions such as rheumatoid arthritis, psoriasis, asthma, inflammatory bowel disease and other diseases mediated by increased levels of prostaglandins, leukotriene, or platelet activating factor. Pharmaceutical compositions of the invention comprise a therapeutically effective amount of a calcium independent cPLA₂ inhibitor compound first identified according to the present invention in a mixture with an optional pharmaceutically acceptable carrier. The term “pharmaceutically acceptable” means a non-toxic material that does not interfere with the effectiveness of the biological activity of the active ingredient(s). The term “therapeutically effective amount” means the total amount of each active component of the method or composition that is sufficient to show a meaningful patient benefit, i.e., healing or amelioration of chronic conditions or increase in rate of healing or amelioration. When applied to an individual active ingredient, administered alone, the term refers to that ingredient alone. When applied to a combination, the term refers to combined amounts of the active ingredients that result in the therapeutic effect, whether administered in combination, serially or simultaneously. A therapeutically effective dose of the inhibitor of this invention is contemplated to be in the range of about 0.1 μg to about 100 mg per kg body weight per application. It is contemplated that the duration of each application of the inhibitor will be in the range of 12 to 24 hours of continuous administration. The characteristics of the carrier or other material will depend on the route of administration.

The amount of inhibitor in the pharmaceutical composition of the present invention will depend upon the nature and severity of the condition being treated, and on the nature of prior treatments which the patient has undergone. Ultimately, the attending physician will decide the amount of inhibitor with which to treat each individual patient. Initially, the attending physician will administer low doses of inhibitor and observe the patient's response. Larger doses of inhibitor may be administered until the optimal therapeutic effect is obtained for the patient, and at that point the dosage is not increased further.

Administration is preferably intravenous, but other known methods of administration for anti-inflammatory agents may be used. Administration of the anti-inflammatory compounds identified by the method of the invention can be carried out in a variety of conventional ways. For example, for topical administration, the anti-inflammatory compound of the invention will be in the form of a pyrogen-free, dermatologically acceptable liquid or semi-solid formulation such as an ointment, cream, lotion, foam or gel. The preparation of such topically applied formulations is within the skill in the art. Gel formulation should contain, in addition to the anti-inflammatory compound, about 2 to about 5% W/W of a gelling agent. The gelling agent may also function to stabilize the active ingredient and preferably should be water soluble. The formulation should also contain about 2% W/V of a bactericidal agent and a buffering agent. Exemplary gels include ethyl, methyl, and propyl celluloses. Preferred gels include carboxypolymethylene such as Carbopol (934P; B.F. Goodrich), hydroxypropyl methylcellulose phthalates such as Methocel (K100M premium; Merril Dow), cellulose gums such as Blanose (7HF; Aqualon, U.K.), xanthan gums such as Keltrol (TF; Kelko International), hydroxyethyl cellulose oxides such as Polyox (WSR 303; Union Carbide), propylene glycols, polyethylene glycols and mixtures thereof. If Carbopol is used, a neutralizing agent, such as NaOH, is also required in order to maintain pH in the desired range of about 7 to about 8 and most desirably at about 7.5. Exemplary preferred bactericidal agents include steryl alcohols, especially benzyl alcohol. The buffering agent can be any of those already known in the art as useful in preparing medicinal formulations, for example 20 mM phosphate buffer, pH 7.5.

Cutaneous or subcutaneous injection may also be employed and in that case the anti-inflammatory compound of the invention will be in the form of pyrogen-free, parenterally acceptable aqueous solutions. The preparation of such parenterally acceptable solutions, having due regard to pH, isotonicity, stability, and the like, is within the skill in the art.

Intravenous injection may be employed, wherein the anti-inflammatory compound of the invention will be in the form of pyrogen-free, parenterally acceptable aqueous solutions. A preferred pharmaceutical composition for intravenous injection should contain, in addition to the anti-inflammatory compound, an isotonic vehicle such as Sodium Chloride Injection, Ringer's Injection, Dextrose Injection, Dextrose and Sodium Chloride Injection, Lactated Ringer's Injection, or other vehicle as known in the art. The pharmaceutical composition according to the present invention may also contain stabilizers, preservatives, buffers, antioxidants, or other additive known to those of skill in the art.

The amount of anti-inflammatory compound in the pharmaceutical composition of the present invention will depend upon the nature and severity of the condition being treated, and on the nature of prior treatments which the patient has undergone. Ultimately, the attending physician will decide the amount of anti-inflammatory compound with which to treat each individual patient.

Anti-inflammatory compounds identified using the method of the present invention may be administered alone or in combination with other anti-inflammation agents and therapies.

EXAMPLE 1 Purification of Calcium Independent cPLA₂

A) Preparation of CHO-Dukx Cytosolic Fraction:

CHO cells, approximately 5×10¹¹ cells from a 250 L culture, were concentrated by centrifugation and rinsed once with phosphate-buffered saline and reconcentrated. the cell slurry was frozen in liquid nitrogen and stored at −80° C. at 4×10¹¹ cells/kg of pellet. The CHO pellets were processed in 0.5 kg batches by thawing the cells in 1.2 L of 20 mM imidazol pH 7.5, 0.25M sucrose, 2 mM EDTA, 2 mM EGTA, 1 g/ml leupeptin, 5 μg/ml aprotinin, 5 mM DTT and 1 mM PMSF (“Extraction Buffer”). The cells were transferred to a Parr bomb at 4° C. and pressurized at 600 psi for 5 minutes and lysed by releasing the pressure. The supernatant was centrifuged at 10,000×g for 30 minutes and subsequently at 100,000×g for 60 minutes.

B) DEAE Anion Exchange Chromatography:

The cytosolic fraction (10 gm protein) was diluted to 5 mg/ml with 20 mM imidazol pH 7.5, 5 mM DTT, 1 mM EDTA and 1 mM EGTA (Buffer A) and applied to a 1 L column of DEAE toyopearl equilibrated in buffer A at 16 ml/min. The column was washed to background absorbance (A₂₈₀) with buffer A and developed with a gradient of 0-0.5M NaCl in buffer A over 240 minutes with one minute fractions. The first activity peak at 100-150 mM NaCl was collected.

C) Hydrophobic Interaction and Heparin Toyopearl Chromatography:

The DEAE fractions (4 gm of protein at 3 mg/ml) were made 0.5M in ammonium sulfate and applied at 10 ml/min to a 300 ml phenyl toyopearl column equilibrated in buffer A containing 0.5M ammonium sulfate. The column was washed to background absorbance (A₂₈₀). The column was then developed with a gradient of 0.5-0.2M (15 minutes) then 0.2-0.0 M ammonium sulfate (85 minutes). The column was then connected in tandem to a 10 ml heparin column equilibrated in buffer A and elution was continued for 18 hours at 1.5 ml/min with buffer A. The phenyl column was disconnected and the activity was eluted from the heparin column by applying 0.5M NaCl in buffer A at 2 ml/min.

D) Chromatofocusing Chromatography:

A portion of the above active fractions (16 mg) was dialyzed exhaustively against 20 mM Bis-Tris pH 7, 10% glycerol, 1M urea and 5 mM DTT and applied at 0.5 ml/min to a Mono P 5/20 column equilibrated with the same buffer. The column was washed with the same buffer to background absorbance (A₂₈₀) and a pH gradient was established by applying 10% polybuffer 74 pH 5, 10% glycerol, 1M urea and 5 mM DTT.

The relative purification of the enzyme of the present invention at each step of the foregoing purification scheme is summarized in Table II. TABLE II Protein Activity Specific Activity Fold Yield Step (mg) (u**) (u/mg) Purification (%) cytosolic 126,000 2050 0.016 — — extract* DEAE 16,000 1264 0.079 5 60 phenyl/ 193 90 0.46 30 4.5 heparin Mono P 0.1-0.2 14 140 8,000 0.7 *Extract from 3.5 kg of frozen CHO cell pellet **1 unit is defined as the amount of activity that releases 1 nmol of arachidonic acid per minute

The phospholipase can be further purified by the following steps:

E) Heparin Chromatography:

The sample from (D) above is applied at 0.5 ml/min onto a heparin column (maximum capacity 10 mg protein/ml of resin), equilibrated in buffer A. The activity is eluted by 0.4M NaCl in buffer A.

F) Size Exclusion Chromatography:

The active fractions from the heparin column are applied to two TSK G3000SW_(XL) columns (7.8 mm×30 cm) linked in tandem equilibrated with 150 mM NaCl in buffer A at 0.3 ml/min. Phospholipase activity elutes in the 250-350 kD size range.

Recombinant enzyme may also be purified in accordance with this example.

EXAMPLE 2 Amino Acid Sequencing

A portion (63 μg total protein) of the Mono P active fractions was concentrated on a heparin column, as described above. The sample, 0.36 ml was mixed with an equal volume of buffer A and 10% SDS, 10 μl and concentrated to 401 on an Amicon-30 microconcentrator. The sample was diluted with buffer A, 100 μl, concentrated to 60 μl and diluted with Laemmli buffer (2×), 40 μl. The solution was boiled for 5 minutes and loaded in three aliquots on a 4-20% gradient SDS-PAGE mini gel. The sample was electophoresed for two hours at 120 v, stained for 20 minutes in 0.2% Blue R-250, 20% methanol and 0.5% acetic acid and destained in 30% methanol (Rosenfeld et. al. Anal. Biochem. 203, pp. 173-179, 1992). Briefly, the protein bands corresponding to the phospholipase were excised from the gel with a razor blade and washed with 4 150 μl aliquots of 200 mM NH₄HCO₃, 50% acetonitrile, for a total of 2 hours. The gel pieces were allowed to air dry for approximately 5 minutes, then partially rehydrated with 1 μl of 200 mM NH₄HCO₃, 0.02% Tween 20 (Pierce) and 2 μl of 0.25 μg/μl trypsin (Promega). Gel slices were placed into the bottom of 500 μl mini-Eppendorf tubes, covered with 30 μl 200 mM NH₄HCO₃, and incubated at 37 C for 15 hours. After 1-2 minutes of centrifugation in an Eppendorf microfuge, the supernatants were removed and saved. Peptides in the gel slices were extracted by agitation for a total of 40 minutes with 2 100 μl aliquots of 60% acetonitrile, 0.1% TFA. The extracts were combined with the previous supernatant. The volume was reduced by lyophilization to about 150 μl, and then the sample was diluted with 750 μl 0.1% TFA. Peptide maps were run on an ABI 130A Separation System HPLC and an ABI 30×2.1 mm RP-300 column. The gradient used was as follows: 0-13.5 minutes 0% B, 13.5-63.5 minutes 0-100% B and 63.5-68.5 minutes 100% B, where A is 0.1% TFA and B is 0.085% TFA, 70% acetonitrile. Peptides were then sequenced on an ABI 470A gas-phase sequencer.

EXAMPLE 3 Phopholipase Assays

1. sn-2 Hydrolysis Assays

A) Liposome: The lipid, e.g. 1-palmitoyl-2-[¹⁴C]arachidonyl-sn-glycero-3-phosphocholine (PAPC), 55 mCi/mmol, was dried under a stream of nitrogen and solubilized in ethanol. The assay buffer contained 100 mM Tris-HCl pH 7, 4 mM EDTA, 4 mM EGTA, 10% glycerol and 25 μM of labelled PAPC, where the volume of ethanol added was no more than 10% of the final assay volume. The reaction was incubated for 30 minutes at 37° C. and quenched by the addition of two volumes of heptane:isopropanol:0.5M sulfuric acid (105:20:1 v/v). Half of the organic was applied to a disposable silica gel column in a vacuum manifold positioned over a scintillation vial, and the free arachidonic was eluted by the addition of ethyl ether (1 ml). The level of radioactivity was measured by liquid scintillation.

Variations on this assay replace EDTA and EGTA with 10 mM CaCl₂.

B) Mixed Micelle Basic: The lipid was dried down as in (A) and to this was added the assay buffer consisting of 80 mM glycine pH 9, 5 mM CaCl₂ or 5 mM EDTA, 10% or 70% glycerol and 200 μM triton X-100. The mixture was then sonicated for 30-60 seconds at 4° C. to form mixed micelles.

C) Mixed Micelle Neutral: As for (B) except 100 mM Tris-HCl pH 7 was used instead of glycine as the buffer.

2. sn-1 Hydrolysis Assays

Sn-1 hydrolysis assays are performed as described above for sn-1 hydrolysis, but using phospholipids labelled at the sn-1 substituent, e.g. 1-[¹⁴C]-palmitoyl-2-arachidonyl-sn-glycero-3-phophocholine.

EXAMPLE 4 Cloning Of Calcium Independent cPLA₂/B

A) cDNA Library Construction

Total RNA was first prepared from 2×10⁸ CHO-DUX cells using the RNAgents total RNA kit (Promega, Madison, Wis.) and further purified using the PolyATract mRNA Isolation System (Promega) to yield 13.2 μg polyA+mRNA. Double stranded cDNA was prepared by the Superscript Choice System (Gibco/BRL, Gaithersburg, Md.) starting with 2 μg of CHO-DUX mRNA and using oligo dT primer. The cDNA was modified at both ends by addition of an EcoRI adapter/linker provided by the kit. These fragments were then ligated into the predigested lambda ZAPII/EcoRI vector, and packaged into phage particles with Gigapack Gold packaging extracts (Stratagene, La Jolla, Calif.).

B) Oligonucleotide Probe Design

Several of the peptide sequences determined for the purified calcium independent PLA₂/B were selected to design oligonucleotide probes. The amino acid sequence from amino acid 361 to 367 of SEQ ID NO:2 was used to design two degenerate oligonucleotide pools of 17 residues each. Pool 1 is 8-fold degenerate representing the sense strand for amino acids 361 to 366 of SEQ ID NO:2, and pool 2 is 12-fold degenerate representing the antisense strand for amino acids 362-367 of SEQ ID NO:2. Two other degenerate pools were also made from other sequences. Pool 3 is 32-fold degenerate and represents the sense strand for amino acids 490 to 495 of SEQ ID NO:2, and pool 4 is 64-fold degenerate representing the antisense strand for amino acids 513 to 518 of SEQ ID NO:2.

C) Library Screening

Approximately 400,000 recombinant bacteriophage from the CHO-DUX cDNA library were plated and duplicate nitrocellulose filters were prepared. One set of filters was hybridized with pool 1 and the other with pool 2 using tetramethylammonium chloride buffer conditions (Jacobs et al., Nature, 1985, 313, 806). Twelve positive bacteriophages were identified and plated for further analysis. Three sets of nitrocellulose filters were prepared from this plating and hybridized with pools 2, 3 and 4; to represent the three peptide sequences from which probes were designed. Several clones were positive for all three pools. Individual bacteriophage plaques were eluted and ampicillin resistant plasmid colonies were prepared following the manufacturer's protocols (Stratagene). Plasmid DNA was prepared for clones 9, 17, 31 and 49, and restriction digests revealed 3.0 kb inserts. Analysis of a portion of the DNA sequence in these clones confirmed that they contained several cPLA₂/B peptide sequences and represented the complete coding region of the gene. Clone 9 was selected for complete DNA sequence determination. The sequence of clone 9 is reported as SEQ ID NO:1.

Clone 9 was deposited with ATCC on Jul. 27, 1994 as accession number 69669.

EXAMPLE 5 Expression Of Recombinant cPLA₂/B

A) Expression in COS Cells

Clone 9 from Example 4 was excised inserted into a SalI site that was engineered into the EcoRI site of the COS expression vector, PMT-2, a beta lactamase derivative of p91023 (Wong et al., Science, 1985, 228, 810). 8 μg of plasmid DNA was then transfected into 1×10⁶ COS cells in a 10 cm dish by the DEAE dextran protocol (Sompayrac et al., Proc. Natl. Acad. Sci. USA, 1981, 78, 7575) with the addition of a 0.1 mM chloroquine to the transfection medium, followed by incubation for 3 hours at 37° C. The cells were grown in conventional media (DME, 10% fetal calf serum). At 40-48 hours post-transfection the cells were washed twice and then incubated at 37° C. in PBS, 1 mM EDTA (5 ml). The cells were then collected by centrifugation, resuspended in Extraction Buffer (0.5 ml), and lysed by 20 strokes in a Dounce at 4° C. The lysate was clarified by centrifugation and 10-50 μl of the cytosolic fraction was assayed in the neutral and pH 9 mixed micelle assays.

In a further experiment, COS cells were transiently transfected according to established procedures (Kaufman et al.). After 40-48 hours post-transfection the cells were labelled with ³⁵S-methionine, 200 μCi per 10 cm plate, for one hour and the cells were lysed in NP-40 lysis buffer (Kaufman et al.). The cell lysates were analyzed by SDS-PAGE on a 4-20% reducing gel where equal counts were loaded per lane. There was an additional protein band at 84-86 kD in the lysates from cells transfected with clones 9, 31 and 49, but not in controls (see FIG. 7).

B) Expression in CHO Cells

A single plasmid bearing both the cPLA₂/B encoding sequence and a DHFR gene, or two separate plasmids bearing such sequences, are introduced into DHFR-deficient CHO cells (such as Dukx-BII) by calcium phosphate coprecipitation and transfection. DHFR expressing transformants are selected for growth in alpha media with dialyzed fetal calf serum. Transformants are checked for expression of recombinant enzyme by bioassay, immunoassay or RNA blotting and positive pools are subsequently selected for amplification by growth in increasing concentrations of methotrexate (MTX) (sequential steps in 0.02, 0.2, 1.0 and 5 μM MTX) as described in Kaufman et al., Mol. Cell Biol., 1983, 5, 1750. The amplified lines are cloned and recombinant enzyme expression is monitored by the mixed micelle assay. Recombinant enzyme expression is expected to increase with increasing levels of MTX resistance.

EXAMPLE 6 Mutagenesis of Serine Residues

Ser252 and Ser465 of the murine cPLA₂/B amino acid sequence were mutated to alanine residues using the Chamelon Mutagenesis kit (Stratagene) using oligonucleotides CATGGGACCCGCTGGCTTTCC (SEQ ID NO:24) and GGCAGGAACCGCCACTGGGGGC (SEQ ID NO:25), respectively. PLA₂ activity was abrogated by changing Ser465 to Ala in the lipase consensus sequence (GXSXGG) surrounding that residue. Although Ser252 is found in a partial lipase motif, mutagenesis did not result in loss of activity. Moreover, Ser465, and the lipase consensus sequence surrounding this residue, are conserved in the human sequence (see amino acids 462-467 of SEQ ID NO:21 and 463468 of SEQ ID NO:23), while Ser252 is not. On this basis, it is believed that this conserved serine residue is required for activity.

Patent and literature references cited herein are incorporated by reference as if fully set forth. 

1.-28. (canceled)
 29. An isolated polypeptide comprising an amino acid sequence encoded by a first polynucleotide, wherein the first polynucleotide hybridizes to the complement of a second polynucleotide in 4×SSC at 65° C., wherein the second polynucleotide is selected from: a) a polynucleotide having the nucleic acid sequence of SEQ ID NO: 16; b) a polynucleotide having the nucleic acid sequence of SEQ ID NO: 18; c) a polynucleotide having the nucleic acid sequence of SEQ ID NO: 20; d) a polynucleotide having the nucleic acid sequence of SEQ ID NO: 22; and wherein the first polynucleotide encodes a polypeptide having enzymatic activity in a mixed micelle assay with 1-palmitoyl-2-[⁴C]-arachidonyl-phosphatidylcholine.
 30. The isolated polypeptide of claim 29, wherein the second polynucleotide has the nucleic acid sequence of SEQ ID NO:
 16. 31. The isolated polypeptide of claim 29, wherein the second polynucleotide has the nucleic acid sequence of SEQ ID NO:
 18. 32. The isolated polypeptide of claim 29, wherein the second polynucleotide has the nucleic acid sequence of SEQ ID NO:
 20. 33. The isolated polypeptide of claim 29, wherein the second polynucleotide has the nucleic acid sequence of SEQ ID NO:
 22. 34. An isolated polypeptide comprising an amino acid sequence encoded by a first polynucleotide, wherein the first polynucleotide hybridizes to the complement of a second polynucleotide in 50% formamide and 4×SSC at 42° C., wherein the second polynucleotide is selected from: a) a polynucleotide having the nucleic acid sequence of SEQ ID NO: 16; b) a polynucleotide having the nucleic acid sequence of SEQ ID NO: 18; c) a polynucleotide having the nucleic acid sequence of SEQ ID NO: 20; d) a polynucleotide having the nucleic acid sequence of SEQ ID NO: 22; and wherein the first polynucleotide encodes a polypeptide having enzymatic activity in a mixed micelle assay with 1-palmitoyl-2-[¹⁴C]-arachidonyl-phosphatidylcholine.
 35. The isolated polypeptide of claim 34, wherein the second polynucleotide has the nucleic acid sequence of SEQ ID NO:
 16. 36. The isolated polypeptide of claim 34, wherein the second polynucleotide has the nucleic acid sequence of SEQ ID NO:
 18. 37. The isolated polypeptide of claim 34, wherein the second polynucleotide has the nucleic acid sequence of SEQ ID NO:
 20. 38. The isolated polypeptide of claim 34, wherein the second polynucleotide has the nucleic acid sequence of SEQ ID NO:
 22. 